Transversely or sidewardly extending, elongate headers of from about 12 feet to 30 feet and greater in length are commonly utilized on agricultural vehicles for cutting and windrowing crops such as cereal grains and other seed crops, as well as grasses. The headers be supported on height control apparatus, e.g. cylinders, or the like, or rest on skid shoes which move along the surface of a field or pasture, to position cutting apparatus of the header, such as an elongate sickle cutter bar or a row of disk cutters, close to the surface for cutting the stalks or stems of crops and grasses close to the surface. A flotation system allows the header to be guided over obstacles and uneven ground without damaging the cutting apparatus of the header.
Header flotation systems typically use a fluid circuit including an accumulator, hydraulic cylinders, and control valves to perform the flotation function. The vehicles may have a single hydraulic cylinder, or one on each side of the header, to perform both a lift and flotation function, or they may have separate hydraulic cylinders for the lift and flotation functions with the capability of independently adjusting the flotation force for each side of the header. Typically the operator selects the desired flotation setting by actuating rocker switches; wherein one switch position reduces header contact force with the ground, and another position increases header contact force with the ground. Once the flotation setting is selected, the control valves will return to this preset flotation condition whenever the flotation mode is selected, regardless of subsequent header lift and lower operations.
One aspect of the operator selected flotation setting is that it determines how quickly the header returns in a controlled acceleration or controlled “fall” to its terrain contact position after rising in response to contact with an elevated feature of the terrain. If the header falls too slowly, regions of the field may not be cut at the desired height. If the header falls too rapidly, however, the header may impact or ride roughly over the ground, thereby resulting in undesirably harsh or jarring ride characteristics. It is also possible that the header could impact the ground in some conditions, such as uneven terrain, with sufficient force to result in damage to the header and/or the crop. Typically, an operator's flotation setting will be a function, at least in part, on the ground speed of the vehicle. As a general rule, when traveling over a swath of uneven terrain at a relatively low speed, terrain following can be achieved at slower header accelerations, compared to a higher speed. Thus, for travel at lower speeds, an operator would likely use a flotation setting to allow the header to fall more slowly than that selected for a higher speed.
During the harvesting operation, the header downward acceleration may vary from the desired characteristic selected by the operator due to factors such as increases or decreases in vehicle ground speed, changes in hydraulic fluid viscosity, and other environmental factors. Another such factor of note is change in effective weight of the header. When the vehicle moves through the field, the header often accumulates plant material, rocks, dirt, sand, sticks, and the like, resulting in a gradual increase in the effective weight of the header. As material gradually accumulates on the header, its return rate is gradually increased accordingly. Eventually, the desired flotation characteristic selected by the operator when the header was clear will be negatively impacted requiring calibration of the flotation system to restore the desired header flotation characteristic. Conversely, during a pause in operation, the operator may clear the header of accumulated material resulting in an abrupt decrease in its effective weight and a slower return to its operating height, again requiring flotation system calibration. In this regard, previous systems have sought to compensate for changing conditions, such as weight changes due to accumulated debris on the header, automatically, by using methods that have been found to be undesirably complex and have other disadvantages.
For instance, some known systems require precise height measurement data at a known time interval to compute an acceleration of the header and/or force measurement data at the header to automatically calibrate the flotation system. Requiring header height or force data is disadvantageous because of the sensors required to obtain the data. Typically sensors that supply height, position, or force data require calibration, at least on installation and replacement, thereby increasing the complexity of the system. In addition, a potential source of error is added to the system. For example, if a sensor is improperly calibrated, incorrect input data will likely result in unsatisfactory system operation. It is therefore desirable to implement a flotation calibration system using measuring devices that do not require calibration and are easy to install and replace.
Thus, what is sought is an automatic system and method for calibrating a header flotation system of an agricultural vehicle that can be employed while the vehicle is in motion, including when traversing a field, which does not rely on, or require calibration of, height and/or pressure sensors, and which overcomes at least one of the problems, shortcomings or disadvantages set forth above.